GPS World, September 2017

SYSTEM SYSTEMS SYS OF Policy and System Developments GPS Galileo GLONASS BeiDou Second QZSS Signal on Air T he second satellite of Japans Quasi Zenith Satel l ite System QZSS has started transmitting navigation signals QZS 2 or Michibiki 2 was launched on June 1 2017 and joins its predecessor QZS 1 Michibiki 1 which has been in orbit since September 2010 Both satellites have been placed into inclined geosynchronous elliptical orbits which enable extended satellite visibility periods over Japan and are characteristic features for this regional navigation system The third satellite QZS 3 was launched on Aug 19 2017 into a geostationary orbit If all goes according to plan a fourth satellite in an eccentric orbit will follow by the end of this year and complete the constellation QZS 2 Signal Tracking It is not straightforward to tell when QZS 2 started signal transmission exactly About four weeks after launch on June 27 between 10 17 and 12 37 UTC several Septentrio PolaRx GNSS receivers in the Asia Pacific region recorded continuous L5 observations About one week later on July 4 shortly after 03 02 UTC Javad and Trimble receivers picked up L1 C A and L5 signals from QZS 2 for a few seconds Then again between 23 03 UTC on July 6 and 01 36 UTC on July 7 several receivers intermittently tracked the L1 C A L2C and L5 signals Finally on July 10 starting at approximately 01 03 UTC these three signals were continuously tracked until approximately 04 00 UTC on July 12 Up until Aug 1 signal CHOF J02 S1C S2X S5X JAVAD TRE_ G3TH DELTA 65 60 55 50 45 40 35 30 25 20 15 10 65 60 55 50 45 40 35 30 25 20 15 10 tracking had remained intermittent but has been stable since This was presumably the result of interruptions in the signal transmission due to test activities The plots in FIGURE 1 show QZS 2 signals as tracked by GNSS receivers in Japan and Australia on July 10 The two first sets of broadcast messages were transmitted on July 16 at 6 00 and 7 00 UTC Regular transmission of broadcast ephemerides started on July 27 at 22 00 UTC but deviations from the hourly update rate still occur from time to time Identical or Fraternal Twins At first glance QZS 2 seems like a look alike of QZS 1 but there are many differences between the two spacecraft Most apparent is the presence of an additional auxiliary antenna Like QZS 1 QZS 2 transmits its navigation signals on the L1 L2 L5 and L band Experiment LEX frequencies through the main antenna while the augmentation signal 10 GPS WORLD WWW GPSWORLD COM SEPTEMBER 2017 39200 39000 38800 38600 38400 38200 38000 37800 37600 37400 37200 37000 36800 44000 42000 40000 38000 36000 34000 L1S formally known as Submeter class Augmentation with Integrity Function or SAIF is transmitted from a separate antenna However the new L5S signal which is introduced with QZS 2 is transmitted with yet another antenna The new satellite also has a shorter wingspan of only 19 meters since it is equipped with two solar panel segments on each side compared to three segments for QZS 1 with a width of 253 meters The second QZSS satellite also follows a different attitude model Unlike QZS 1 which switches between yaw steering mode and orbit normal mode depending on the suns elevation angle with respect to the orbit plane QZS 2 always remains yaw steering except for short periods of time when orbit maneuvers are performed Further differences will become apparent in the analysis of the signal spectra in the subsequent sections The Cabinet Office of the Government of Japan which oversees QZSS as a 5 C N 0 dB Hz 36600 Pseudorange kilometers UNX2 J02 S1C S2X S5X JAVAD TRE_ G3TH DELTA 5 C N 0 dB Hz 2017 07 10 10 July 6h 12h 18h 32000 Pseudorange kilometers Figure 1 QZS 2 signals tracked by GNSS receivers in Chofu Japan top plot and Sydney Australia bottom plot The plots depict the measured C N 0 for L1 C A black L2C red and L5 green together with the observed pseudorange grey The frequent discontinuities in the pseudorange are due to the receiver clock adjustments Both receivers exhibited a short tracking outage at approximately 06 00 UTC The interruption in tracking at Chofu around 08 00 UTC is due to the low elevation angle of the satellite

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